Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

2. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

3. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Compressor and condenser

Receiver and evaporator

Condenser and receiver

4. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

5. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Piston type reciprocating

Centrifugal

6. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

9: 1

1: 9

7. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

8. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

9. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Low boiling point

Large latent heat

Good electrical conductor

10. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

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11. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

Sub-cooling or under-cooling

None of these

12. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these

13. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Equally

Unpredictable

14. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

4.33

3.33

15. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

None of these

Negative

Positive

16. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

17. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Equal to unity

Any one of the above

18. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

19. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

20. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

One heat exchanger

Two heat exchangers

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21. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

22. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Any value

Low

23. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

24. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

25. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Carbon dioxide

Brine

26. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

27. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Relative humidity

28. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

29. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.6

0.376

0.4

30. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

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31. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

32. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

33. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

30 bar

15 bar

34. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

35. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

36. Rating of a domestic refrigerator is of the order of

5 tons

40 tons

10 tons

0.1 ton

37. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

38. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Carnot

Bell Coleman

39. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

Above critical temperature

40. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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